1. Field of the Invention
The present invention relates to a macro lens system that can be used when carrying out a photographic operation while focusing on an object at infinity to an object at a close distance.
2. Description of Related Art
Various types of focusing systems for a macro lens system are known in the art, for example, a totally telescoping lens system (totally retractable/extendable lens system), a front-lens-group telescoping lens system (front-lens-group retractable/extendable lens system), an internal focusing lens system, and a floating lens system, etc. Out of such types of focusing systems, in an internal-focusing macro lens system in which, during a focusing operation, a frontmost lens group provided closest to the object side is stationary with respect to the imaging plane and a plurality of lens groups other than the frontmost lens group independently move in the optical axis direction, there is the advantage of the center-of-gravity of the lens system having little change during focusing on (photographing) an object at a close distance, due to the overall length of the lens system always being constant, so that the lens barrel does not extend outwards and contact the object (subject) during the focusing operation. However, an internal-focusing macro lens system has the disadvantages of having a large number of lens elements, the optical performance thereof being easily deteriorated, and the mechanism therefor being complicated.
Whereas, in a floating macro lens system, in which the first lens group and the second lens group advance/retract (in the optical axis direction) by mutually different movement amounts, there are advantages such as the number of lens elements being few, the optical quality not easily deteriorating due to manufacturing error, and the structure thereof being simple.
Furthermore, in recent years, macro lens systems are also known to have an image-stabilization function (anti-shake function/shake-correction function) in which part of the lens system thereof is moved (decentered) in directions orthogonal to the optical axis to displace the imaging position in order to correct changes in the object-image position that occur due to hand shake, etc., and a number of floating macro lens systems in which the movement amounts of the first lens group and the second lens group differ when advancing/retracting have been proposed (Japanese Unexamined Patent Publication Nos. H07-152001, H07-261126, 2009-145588 and H09-218349).
However, in Japanese Unexamined Patent Publication No. H07-152001, since the entire second lens group serves as an image-stabilizing lens group (image-shake correction lens group), the weight of the image-stabilizing lens group is great (heavy), thereby increasing the burden on the image-stabilizing mechanism (image-shake correction mechanism) therefor.
In Japanese Unexamined Patent Publication Nos. H07-261126 and 2009-145588, although a plurality of lens elements, that constitute part of a second lens group, serve as an image-stabilizing lens group, a sufficient reduction in weight cannot be achieved, so that a large mechanical burden on the image-stabilizing mechanism still remains. Furthermore, due to the inappropriate refractive-power balance between the image-stabilizing lens group within the second lens group and the remaining lens groups, various aberrations such as spherical aberration and coma, etc., occur, thereby deteriorating the optical quality during an image-stabilizing operation (image-shake correction operation), or the amount of movement of the image-stabilizing lens group becomes too large, so that the burden on the image-stabilizing mechanism increases.
In Japanese Unexamined Patent Publication No. H09-218349, a reduction in weight of the image-stabilizing lens group is achieved configuring part of a first lens group as an image-stabilizing lens group. However, in a floating macro lens system, since the imaging function is mainly provided in the first lens group, if the first lens group is divided into an image-stabilizing sub-lens group and a remaining sub-lens group, the optical quality can easily deteriorate due to manufacturing error.